Year	Years
1970	0.41
1971	0.43
1972	0.44
1973	0.46
1974	0.48
1975	0.5
1976	0.52
1977	0.54
1978	0.56
1979	0.58
1980	0.61
1981	0.63
1982	0.66
1983	0.69
1984	0.71
1985	0.74
1986	0.78
1987	0.81
1988	0.84
1989	0.88
1990	0.92
1991	0.96
1992	1
1993	1.05
1994	1.1
1995	1.15
1996	1.2
1997	1.25
1998	1.31
1999	1.36
2000	1.42
2001	1.48
2002	1.53
2003	1.59
2004	1.65
2005	1.71
2006	1.77
2007	1.84
2008	1.9
2009	1.97
2010	2.03
2011	2.1
2012	2.17
2013	2.24
2014	2.31
2015	2.38